1. Field of the Invention
The present invention relates generally to a display in a portable radio terminal, and in particular, to an interface circuit of a color LCD (Liquid Crystal Display) for displaying pictures or characters.
2. Description of the Related Art
As the performance of communication terminals (mobile phones) improves, they are capable of transmitting not only voice communication but also data and image communication as well. To provide the image communication service, the standard character-type black and white LCD is replaced with a color LCD. Because of the large power dissipation of an OSD (On Screen Display), the typical television OSD is difficult to apply to a communication terminal (mobile phone) which requires minimum power consumption. A low power consumption alternative, like the LCD, is needed. Unfortunately, the conventional control devices cannot be applied to the color LCD, therefore, a new color LCD interface is needed. While constructing an RGB (Red, Green, Blue) signal and a synchronization circuit represents a significant undertaking, the present invention addresses this problem.
It is, therefore, an object of the present invention to provide an interface circuit in a portable radio terminal (mobile phone) for interfacing between a color LCD controller and a portable radio terminal controller. The output circuit consists of a signal suitable for a conventional LCD controller or a color LCD. A conventional character-type LCD may therefore be replaced with a color LCD without incident.
To achieve the above, there is provided a color LCD interface circuit for outputting an RGB signal for an intended image and either a synchronization signal for horizontal and vertical synchronization or a composite synchronization signal to a color LCD controller in a portable radio terminal. The interface circuit is compatible with portable radio terminals having either a color LCD and a controller or a character-type black and white LCD. In the color LCD interface circuit, a first memory stores data needed to execute a color LCD interface program and to represent fonts and color. A main controller reads the color LCD interface program from the first memory and executes the color LCD interface program while a second memory stores a page of image information generated during the execution of the color LCD interface program. A multiplexer selects one of the input signals according to whether a graphical display on the color LCD is an image or represents the operational status of the portable radio terminal. A color processor receives various commands and index data from the controller and generates an internal composite synchronization signal and a digital RGB signal.